On Ubuntu 18.04 in LibreOffice Write I right-click and image and select "Edit with external tool" which fires up Gimp. After editing the image in Gimp I select File -> Overwrite [random].jpg which is supposed to replace the edited image in Writer with the new version. However, in Writer the original image is replaced with an empty box containing the message "Read Error". This behaviour is consistent and reproducible.
I repro with GIMP, but not with Gwenview. Tested also on Windows and with Irfanview it works fine. Arch Linux 64-bit Version: 6.3.0.0.alpha0+ Build ID: e77beebb0d839f5dc0d4f9c4fd7cc9b7ccfd0175 CPU threads: 8; OS: Linux 4.20; UI render: default; VCL: gtk3; Locale: fi-FI (fi_FI.UTF-8); UI-Language: en-US Calc: threaded Built on 16 February 2019
Bah, forgot to search for dupes *** This bug has been marked as a duplicate of bug 119479 ***